According to the knock phenomenon of transmission gear, it is mainly divided into bench test and real vehicle test.
In view of the fact that the transmission gear knock occurs in the specific working condition of the real vehicle, it is difficult to control by using the real vehicle road test, and the microphone and acceleration sensor are not well arranged, domestic and foreign researchers mostly use the bench test to carry out the gear knock test. Forecelli and other scholars establish a virtual engine test device which can simulate the different speed fluctuation amplitude under the second-order harmonic of the engine, The second-order harmonic speed fluctuation simulated by the device is consistent with the engine speed fluctuation measured by the real vehicle test. Using the virtual engine test device, the test results of the acceleration sensor and the near-field microphone of the transmission case under different speed fluctuation amplitude are studied and compared with the main evaluation results, Crowther et al  set up a kind of test device of transmission gear knock. The drive motor is directly connected with the input end of the transmission through the universal joint. By controlling the drive motor to output at a constant speed and using the universal joint to generate periodic torque fluctuation, the engine torque fluctuation input is simulated. Its limitation is under the constant torque control, The peak value of the output torque fluctuation of the driving motor is less than 2n · m, which makes it difficult to simulate the real situation of the vehicle. Robin et al. Set up a transmission knock test bench, load the motor to simulate the power input (including torque and speed input), load the motor to simulate the load. When testing different operating points and different gears, Under the specific torque input of the transmission, the angular speed deviation percentage and the change of the inertia moment of the loose gear in each gear are analyzed, so as to find out the maximum value of the dragging moment of each gear (the knock intensity threshold); through the sensitivity analysis, the influence rule of the average value of the input shaft speed, the average torque of the input shaft, the different gears and the different excitation frequency of the input shaft on the knock intensity threshold is obtained, It provides experimental basis for the establishment of simulation model. Many researchers and mechanisms gradually began to pay attention to the impact of gear lubrication characteristics on the knock strength. For example, Axel Baumann et al.  set up a single pair of gear impact analysis test bench to analyze the knock strength under different viscosity of lubricating oil. The results show that when the input shaft angular acceleration takes a larger value, Using high viscosity lubricating oil can effectively restrain gear knocking. In China, Feng Zhendong et al. Used a semi anechoic chamber to carry out knocking test on a diesel vehicle at idle speed, and measured the near-field noise sound pressure of transmission, acceleration of transmission shell wall, flywheel angular speed and the time history of transmission intermediate shaft angular speed under two working conditions of clutch engagement and separation, Through the correspondence analysis of the peak value of the envelope, it is found that the noise comes from the transmission. Four kinds of clutch shock absorbers are compared and analyzed. It is found that one of the clutch shock absorbers can reduce the sound pressure level of the idle noise by about 3dB (a). Wang Liansheng et al.  built the transmission platform under the constraint state corresponding to the simulation model, and measured the vibration acceleration data of the measuring points on the surface of the transmission by using the acceleration sensor, The spectrum analysis results of the test signals correspond to the spectrum analysis results of the simulation model, thus verifying the multi-body dynamics simulation model of the transmission in this paper. Cai Longsheng et al. Set up an automobile transmission knock noise test bench to simulate the real vehicle working condition, and the driving motor to simulate the four cylinder four stroke engine to provide an ideal excitation source for the transmission, The load motor cooperates with the speed increaser and inertia plate to simulate the resistance moment when the real vehicle is running. The frequency sweep test of the transmission is carried out by using the device, and the envelope demodulation post-processing method is used for the vibration signal. The characteristics of the gear knocking phenomenon are obtained, and the knock phenomenon of each gear is qualitatively determined.
For the real vehicle test, Tian Xiong and other researchers studied the transmission test analysis method based on the structural transmission path. Through the acoustic vibration transmission function test analysis of the noise from the transmission shell to the vehicle interior, it was determined that the transmission gear knock noise was mainly structural noise. By optimizing the clutch lock and the shift lock, some improvement methods were provided for improving the transmission knock noise of the vehicle, Xu xuchu et al. Found that there was gear knock in the transmission of a vehicle under creeping condition through subjective evaluation. By adding a level of stiffness in the pre damping area and the main damping area of the original clutch torsional damper, it can be found from the input shaft speed signal of the engine and transmission that compared with the original level II torsional damper, The phenomenon of gear knocking is effectively improved under the working condition of crawling. Knabe et al. Carry out the real car test on the single axle chassis dynamometer in the semi anechoic room. According to the working condition of the real car transmission knocking phenomenon, collect the engine signal, the transmission oil temperature signal, the sound pressure signal at the two ears of the cab, the primary and secondary speed signals of the flywheel, Taking the engine speed and torque signals as the input of bench test, the knocking strength of the same transmission on different devices is qualitatively determined. The collected sound pressure signals are analyzed by envelope analysis, and the results of envelope analysis are taken as objective evaluation indexes, and the subjective and objective evaluation results are analyzed by regression analysis, A quantitative relationship between subjective and objective evaluation indexes is established. The arrangement of test devices and post-processing methods in this document can be used for reference in transmission real vehicle test.